The present invention relates to a semiconductor device. Particularly, the invention is concerned with a technique applicable effectively to a semiconductor device for which are required signal transmission at a high frequency and high-speed signal transmission in a wide frequency band.
For a package on which is mounted a semiconductor chip with high-speed LSI formed thereon such as IC for optical communication there is required signal transmission of a broad band from DC up to an actually-used high frequency band. Particularly, at a bit rate of 10 Gbits/sec or more, both impedance matching at a high frequency and a low loss are required for such a package as referred to above. To meet such requests it may be effective to adopt means wherein a semiconductor chip is mounted by face-down method onto a main surface of a package substrate with signal transmission lines formed thereon and one ends of the signal transmission lines are extended up to just under electrode pads formed on the main surface of the semiconductor chip, thereby connecting the signal transmission lines and the electrode pads with each other electrically through bump electrodes. According to this means, the signal transmission lines and the semiconductor chip can be connected together at a shortest distance, so that transmission characteristics from the signal transmission lines to the electrode pads on the semiconductor chip can be maintained in a satisfactory condition. By using a ceramic material as a packaging material it is possible to form impedance-matched transmission lines of a low signal loss. Moreover, by making hermetic seal with use of a ceramic material as a packaging material it is possible to protect the semiconductor chip from the external environment and realize a package superior in all of mechanical strength, moisture resistance, heat resistance, and heat dissipating characteristic.
For example in Japanese Unexamined Patent Publication No. Hei 7(1995)-147352 there is disclosed a technique in which the width of a signal transmission line formed on a package substrate is narrowed in an area overlapping a semiconductor chip to compensate a lowering of impedance which is attributable to a capacitance formed between the semiconductor chip and the signal transmission lines, thereby attaining a characteristic impedance matching of the signal transmission lines in the package. Also disclosed therein is a technique which uses a ceramic package substrate to diminish a loss of transmission signal in the package.